capacitor multipliers

dear friends
I have a question that I would like to ask its in three parts
I have been working a great deal with transmitter circuit RF oscillators
way up high in the GHz range and as many people know there are limits
to the coil values and capacitor values that can be used
so when this problem happens I use the old law of putting capacitors in series
to lower the capacitance even more and fixed value inductors in parallel to make
smaller inductance and when both are in parallel they work and transmit
of course this resonate circuit is fed from an external coupled coil because at the frequency range being used the oscilator could not take it so I use mutual inductance


now the second part of my question is this I have read a great deal about capacitor multipliers and how they increase capacitance using op amps and some of the designs of these circuits have the capacitor tapped going into the op amp
also as the output so nearly work like a real capacitor

the thing is I don't want to make capacitance larger I want to make it smaller
then 1pf can you reverse the arrangement of the op amp circuit to make this happen

and is it also possible connect an inductor in parallel with that capacitor multiplier to make a resonance circuit as with a normal LC arrangement

and finely is it possible to cascade capacitor multiplier circuits so that the output of one feeds the input of the next stage even more thanks for your help
best wishes to all

In the high GHz range, stray capacitance can easily swamp anything else. Check the Self Resonant Frequency (SFR) of any inductors that you are using. That should be a lot higher than the frequencies you want the circuit to be tuned at.

Op amps will only work to 100 MHz or so, many will only work to much lower frequencies, so making a virtual capacitor with an op amp will not work.

thank you for all your help appreciated

dear diver 300
thank you for all the useful information
it will be of great help in my research many thanks and
gratefully appreciated
paul666